Planar waveguide display devices are often used in head-up displays (HUD) and helmet-mounted displays for allowing image-bearing light to be displayed as part of a luminous display, to be output through a transparent, planar surface towards the eye of the user. The user is able to view an external scene and image-bearing light output through the transparent planar waveguide concurrently. The result is a luminous display that is perceived as superimposed upon the normal external scene. The display may comprise navigational information, or vehicle control information, for example, which a controller of a vehicle (e.g. a pilot) may thereby perceive whilst maintaining sight of the external scene.
However, the display light output by a planar waveguide display is typically inherently collimated and as a result requires the user to focus at infinity to be able to perceive a luminous display clearly. This may be uncomfortable in practice if the external scene demands a different focus. Furthermore, all perceived elements of a typical such luminous display will share the same focus and this can render visual separation or distinction of separate parts of the display difficult.
The present invention aims to provide an improved display device and/or method.